A Dougal says, plus - Borerays are very rare so think carefully which ones you want to keep entire (probably too late this year

). For the Combined Flock Book of the RBST, which is where you will be birth notifying and registering your stock, you only need to birth notify them at the moment. We usually register our females at the same time then wait until later, once we can see what the tup lambs are like, before we register them. I think that for the CFB there may be a time limit on registrations - not sure how long, maybe 3 years. You can't register wethers.
You are right that it is very expensive to register tups in the CFB - the theory is so that you only register those which are really worthy. However, for these rare breeds we should ideally be breeding one tup to one ewe

to maintain maximum genetic diversity. No-one does this although with our Hebrideans we breed in small groups of 2 to 5 per tup, which is better than 40 ewes per tup.